The person skilled in the art is familiar with systems of TAWS type, “Terrain Awareness and Warning System”. The aim of these systems is to generate an alert when the aircraft is in a dangerous situation where the operational margins are no longer complied with. TAWSs in the guise of autonomous computer or integrated with the functions of TCAS standing for “Traffic Collision Avoidance System”, and WXR standing for “Weather Band X Radar”, in an ISS, “Integrated Surveillance System”, fulfil a primary function of terrain anticollision monitoring (“Safety Net”) and are aimed at emitting audible alerts during an exceptional approach to the relief allowing the crew to react by engaging a vertical resource before it is too late. Accordingly, TAWS systems, decoupled from navigation systems, proceed in two ways. They periodically compare the theoretical trajectory that would be described by the aircraft during a resource and compare it with a section of the terrain and with the obstacles overflown obtained from a digital model of the world or local terrain embedded aboard the computer. Or else, certain TAWSs also integrate modes termed “reactive modes” which, by periodically comparing certain of the current parameters of the craft, for example the radio-altitude and the vertical speed, various charts determine whether the current situation of the aircraft is a normal situation or whether it is potentially dangerous. In the latter case, an alert, limited to a verbal message, is generated to inform the crew. The availability of a terrain model permits functions making it possible to improve the crew's situation perception. Among them, the objective of the alert lines is to delimit the terrain zones for which a TAWS alert might occur. For their part, the “Alert Areas” show the zones causing a TAWS alert.
Numerous patent documents describe this type of system. Among them may be cited patent “EP0 565399B1” describing all the basic concepts of TAWSs and patent application “US2003/0107499A1” describing a device for displaying the terrain risk zones capable of causing a TAWS alert.
The functions carried out by a TAWS are insufficient to protect a craft in relation to obstacles. The alert function of a TAWS system triggers a message destined for the crew as soon as a certain safety threshold is crossed. For the TAWS systems for which a representation of the discrepancy is provided, said representation is limited to the discrepancy with respect to the relief and does not take the obstacles into account. This representation, combined with the other information provided by the system, is difficult to interpret directly and requires thought on the part of the crew to determine the secure zones.
There also exist systems of “HELLAS” type that are able to fulfil a function of protecting against collisions between the craft and an obstacle, notably high-voltage lines, by preventing the aircraft from approaching the obstacle. They proceed by scanning the zone situated generally at the front of the craft by means of a laser beam invisible to the naked eye. The potential obstacles encountered are presented to the pilot via a cockpit display. An audio alert is optionally generated when the craft is considered to be too close to the obstacle. These systems exhibit drawbacks since they are complex and expensive and moreover do not make it possible to represent the risk zones.